Coupled electrochromic compounds with photostable dication oxidation states

ABSTRACT

Coupling of anodic electrochromic compounds by a covalent bond or a bridge link which provides for electronic communication between the coupled electrochromic compounds results in coupled electrochromic compounds which exhibit greater stability as well as electrochromic activity that differs from the monomeric electrochromic compounds. Extension of the absorption spectrum into the near-infrared region of the spectrum is frequently observed. The coupled electrochromic compounds are highly suitable for use in electrochromic media used to produce electrochromic devices.

TECHNICAL FIELD

The present application relates to anodic electrochromic materials. Moreparticularly, the present invention relates to coupled anodicelectrochromic compounds wherein two or more monomeric electrochromiccompounds are coupled to give a new anodic compound with improvedproperties over the monomeric electrochromic compounds.

BACKGROUND ART

Electrochromic devices, and electrochromic media suitable for usetherein, are the subject of numerous U.S. patents, including U.S. Pat.No. 4,902,108, entitled “Single-Compartment, Self-Erasing,Solution-Phase Electrochromic Devices, Solutions for Use Therein, andUses Thereof”, issued Feb. 20, 1990 to H. J. Byker; Canadian Pat. No.1,300,945, entitled “Automatic Rearview Mirror System for AutomotiveVehicles”, issued May 19, 1992 to J. H. Bechtel et al.; U.S. Pat. No.5,128,799, entitled “Variable Reflectance Motor Vehicle Mirror”, issuedJul. 7, 1992 to H. J. Byker; U.S. Pat. No. 5,202,787, entitled“Electro-Optic Device:, issued Apr. 13, 1993 to H. J. Byker et al.; U.S.Pat. No. 5,204,778, entitled “Control System For Automatic RearviewMirrors”, issued Apr. 20, 1993 to J. H. Bechtel; U.S. Pat. No.5,278,693, entitled “Tinted Solution-Phase Electrochromic Mirrors”,issued Jan. 11, 1994 to D. A. Theiste et al.; U.S. Pat. No. 5,280,380,entitled “UV-Stabilized Compositions and Methods”, issued Jan. 18, 1994to H. J. Byker; U.S. Pat. No. 5,282,077, entitled “Variable ReflectanceMirror”, issued Jan. 25, 1994 to H. J. Byker; U.S. Pat. No. 5,294,376,entitled “Bipyridinium Salt Solutions”, issued Mar. 15, 1994 to H. J.Byker; U.S. Pat. No. 5,336,448, entitled “Electrochromic Devices withBipyridinium Salt Solutions”, issued Aug. 9, 1994 to H. J. Byker; U.S.Pat. No. 5,434,407, entitled “Automatic Rearview Mirror IncorporatingLight Pipe”, issued Jan. 18, 1995 to F. T. Bauer et al.; U.S. Pat. No.5,448,397, entitled “Outside Automatic Rearview Mirror for AutomotiveVehicles”, issued Sep. 5, 1995 to W. L. Tonar; and U.S. Pat. No.5,451,822, entitled “Electronic Control System”, issued Sep. 19, 1995 toJ. H. Bechtel et al., each of which patents is assigned to the assigneeof the present invention and the disclosures of each of which are herebyincorporated herein by reference, are typical of modern day automaticrearview mirrors for motor vehicles. These patent references describeelectrochromic devices, their manufacture, and electrochromic compoundsuseful therein, in great detail.

While numerous electrochromic devices are possible, the greatestinterest and commercial importance are associated with electrochromicwindows, electronic displays, light filters and mirrors. A briefdiscussion of these devices will help to facilitate an understanding ofthe present invention.

Electrochromic devices are, in general, prepared from two parallelsubstrates coated on their inner surfaces with conductive coatings, atleast one of which is transparent such as tin oxide, or the like. Thetwo substrates of the device are separated by a gap or “cavity”, intowhich is introduced the electrochromic medium. A commercially availableelectrochromic medium typically contains a solvent and at least oneanodic and/or cathodic electrochromic compound which changes color uponelectrochemical oxidation or reduction. Upon application of a suitablevoltage between the electrodes, the electrochromic compounds areoxidized or reduced depending upon their redox type, changing the colorof the electrochromic medium. The electrochromic compounds change from acolorless or near colorless state to a colored state. Upon removal ofthe potential difference between the electrodes, the electrochemicallyactivated redox states of electrochromic compounds react, becomingcolorless again, and “clearing” the device.

In electrochromic mirrors, devices are constructed with a reflectingsurface located on the outer surface of the substrate which is mostremote from the incident light (i.e. the back surface of the mirror), oron the inner surface of the substrate most remote from the incidentlight. Thus, light striking the mirror passes through the frontsubstrate and its inner transparent conductive layer, through theelectrochromic medium contained in the cavity defined by the twosubstrates, and is reflected back from a reflective surface as describedpreviously. Application of voltage across the inner conductive coatingsresults in a change of the light reflectance of the mirror.

In electrochromic devices, including windows and mirrors, the selectionof the components of the electrochromic medium is critical. The mediummust be capable of reversible color changes over a life cycle of manyyears, including cases where the device is subject to high temperaturesas well as exposure to ultraviolet light.

A variety of anodic electrochromic compounds are available, among whichare the 5,10,-dihydrophenazines, their phenothiazine analogs, and bothring-substituted as well as heteroatom-substituted derivatives. Forexample, 5,10-dimethyl-5,10-dihydrophenazine:

is a well known electrochromic compound. When this compound is oxidizedto the 1+ oxidation state, the compound exhibits a weak absorption bandat ˜700 nm and a more intense, but still modest, absorbance at ˜450 nmin the visible region of the visible spectrum.

The compound can be oxidized at higher potentials to the more highlyoxidized 2+ species, which is more susceptible to both thermal and photodegradation. Moreover, some 2+ species can exist even in devices wherethe applied voltage is well controlled and less than that required fordirect oxidation, (e.g. by disproportionation of 1+ species).

Heretofore, electrochromic devices have not found wide acceptance asarchitectural windows, where darkening during daylight hours (thus beingsubject to UV exposure in their activated state) is a frequentoccurrence. Electrochromic devices used in these environments have showna tendency to degrade over time, even when UV absorbing coatings andadditives are used in attempts to mitigate these effects. Thus the needexists for electrochromic devices that have the stability desired forapplications such as architectural windows and glazings for automobiles.Additionally it is desirable to obtain anodic electrochromic materialswith more intense absorbances in the visible as well as absorbances inthe near-infrared regions of the electromagnetic spectrum.

DISCLOSURE OF INVENTION

It has now been surprisingly discovered that properly bridging two ormore anodic monomeric electrochromic compounds can afford coupledelectrochromic compounds with electrochemically activated forms thathave enhanced photochemical stability. Such coupled electrochromiccompounds also have electrochemical properties and absorption propertiesdifferent than their uncoupled analogs, and in many cases, are found toexhibit absorbance in the near-infrared region of the spectrum.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of an electrochromic device.

FIG. 2 is a plot of a voltammogram showing the electrochemical oxidationof 5,10-dimethyl-5,10-dihydrophenazine.

FIG. 3 is a plot of a voltammogram showing the electrochemical oxidationof 2,2′-bis(5,10-dimethyl-5,10-dihydrophenazine).

FIG. 4 is a plot of a voltammogram showing the electrochemical oxidationof 1,4-bis(5,10-dihydro-5-butyl-10-phenazine)benzene.

FIG. 5 is the absorbance spectrum of the5,10-dimethyl-5,10-dihydrophenazine cation, and the dication of2,2′-bis(5,10-dimethyl-5,10-dihydrophenazine), respectively.

FIG. 6 is the absorbance spectrum of the1,4-bis(5,10-dihydro-5-butyl-10-phenazine)benzene dication.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a cross-sectional view of an electrochromic device 110,which may be a mirror, a window, a display device, and the like. Device110 has a front transparent element 112 having a front surface 112 a anda rear surface 112 b, and a rear element 114 having a front surface 114a and a rear surface 114 b. Since some of the layers of the device arevery thin, the scale has been distorted for pictorial clarity. Also, forclarity of description of such a structure, the following designationswill be used hereinafter. The front surface 112 a of the front elementwill be referred to as the first surface and the back surface 112 b ofthe front element as the second surface. The front surface 114 a of therear element will be referred to as the third surface, and the backsurface 114 b of the rear element as the fourth surface.

Front transparent element 112 may be any material which is transparentand has sufficient strength to be able to operate in the conditions,e.g., varying temperatures and pressures, commonly found in theenvironment of the intended use. Front element 112 may comprise any typeof borosilicate glass, soda lime glass, float glass or any othermaterial, such as, for example, a polymer or plastic such as Topaz®,available from Ticoma, Summit N.J., that is generally transparent in thevisible region of the electromagnetic spectrum. Front element 112 ispreferably a sheet of glass with a thickness ranging from 0.5millimeters (mm) to about 12.7 mm. Rear element 114 must meet theoperational conditions outlined above, except that if the electrochromicdevice is a mirror, rear element 114 does not need to be transparent,and therefore may comprise polymers, metals, glass, ceramics, andpreferably is a sheet of glass with a thickness ranging from 0.5 mm toabout 12.7 mm. If the front and/or rear elements 112 and 114 comprisesheets of glass, the glass can be tempered prior to or subsequent tobeing coating with the layers of electrically conductive material (116and 120).

One or more layers of a transparent electrically conductive material 116are deposited on the second surface 112 b to act as an electrode.Transparent conductive material 116 is desirably a material that: issubstantially transparent to visible light; bonds well to front element112 and maintains this bond when the sealing member 118 bonds thereto;is resistant to corrosion by any materials within the electrochromicdevice; is resistant to corrosion by the atmosphere; and has minimaldiffuse or specular reflectance and good electrical conductance.Transparent conductive material 116 may be fluorine doped tin oxide(FTO), tin doped indium oxide (ITO), ITO/metal/ITO (IMI) as disclosed in“Transparent Conductive Multilayer-Systems for FPD Applications”, by J.Stollenwerk, B. Ocker, K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany,and the materials described in above-referenced U.S. Pat. No. 5,202,787,such as TEC 20 or TEC 15, available from Libbey Owens-Ford Co. (LOF) ofToledo, Ohio. Co-pending U.S. Patent Application entitled “An ImprovedElectro-Optic Device Including A Low Sheet Resistance, High TransmissionTransparent Electrode” describes a two layer, low sheet resistance, hightransmission, scratch resistant transparent electrode that forms strongbonds with adhesives, is not oxygen sensitive, and can be bent to formconvex or aspheric electro-optic mirror elements or tempered in airwithout adverse side effects. The disclosure of this commonly assignedApplication is hereby incorporated herein by reference. Similarrequirements are needed for the layer 120 deposited onto the thirdsurface 114 a, whether it is a transparent conductive material used inelectrochromic windows and in mirrors having a fourth surface reflector(120′), or a combined reflector/electrode used in electrochromic mirrorshaving a third surface reflector, in such case no fourth surface coatingis necessary.

The coating 120 of the third surface 114 a is sealably bonded to thecoating 116 on the second surface 112 b near the outer perimeter by asealing member 118, thereby defining a chamber 122. The coating 120 onthe third surface may vary depending on the final use of the device 110.If the device 110 is an electrochromic window, the coating 120 ispreferably a transparent conductive coating similar to coating 116. If,however, device 110 is an electrochromic mirror, then coating 120 may beeither a transparent conductive coating similar to coating 116 (in whichcase the reflector is placed on the fourth surface), or coating 120 maybe a layer of a reflecting material in accordance with the teachings ofU.S. Pat. No. 5,818,625, herein incorporated by reference. Typicalcoatings for the third surface reflector are chrome, rhodium, silver,silver alloys and combinations thereof.

Sealing member 118 may be any material which is capable of adhesivelybonding the coatings on the second surface 112 b to the coatings on thethird surface 114 a to seal the perimeter such that electrochromicmedium 124 does not leak from chamber 122. Optionally, the layer oftransparent conductive coating 116 and the layer 120 on the thirdsurface 114 a may be removed over a portion where sealing member 118 isdisposed, but generally not the entire portion, otherwise the drivepotential would be difficult to apply to the two coatings. When theconductive coatings are removed, sealing member 118 must bond well toglass.

The performance requirements for a perimeter seal member 118 used in anelectrochromic device are similar to those for a perimeter seal used ina liquid crystal device (LCD) which are well known in the art. The sealmust have good adhesion to glass, metals and metal oxides, must have lowpermeabilities for oxygen, moisture vapor and other detrimental vaporsand gases, and must not interact with or poison the electrochromic orliquid crystal material it is meant to contain and protect. Theperimeter seal can be applied by means commonly used in the LCD industrysuch as by silk-screening or dispensing. Totally hermetic seals such asthose made with glass frit or solder glass can be used, but the hightemperatures involved in processing (usually near 450-degreesCentigrade) this type of seal can cause numerous problems such as glasssubstrate warpage, changes in the properties of transparent conductiveelectrode and oxidation or degradation of the reflector. Because oftheir lower processing temperatures, thermoplastic, thermosetting, or UVcuring organic sealing resins are preferred. Such organic resin sealingsystems for LCD's are described in U.S. Pat. Nos. 4,297,401, 4,418,102,4,695,490, 5,596,023 and 5,596,024. Because of their excellent adhesionto glass, low oxygen permeability and good solvent resistance, epoxybased organic sealing resins are preferred. These epoxy resin seals maybe UV curing, such as described in U.S. Pat. No. 4,297,401, or thermalcuring, for example mixtures of liquid epoxy resin with liquid polyamideresin or dicyandiamide, or may be homopolymerized. The epoxy resin maycontain fillers or thickeners to reduce flow and shrinkage such as fumedsilica, silica, mica, clay, calcium carbonate, alumina, etc., and/orpigments to add color. Fillers pretreated with hydrophobic or silanesurface treatments are preferred. Cured resin crosslink density can becontrolled by use of mixtures of mono-functional, di-functional andmulti-functional epoxy resins and curing agents. Additives such assilanes or titanates can be used to improve the seal's hydrolyticstability and spacers such as glass beads or rods can be used to controlfinal seal thickness and substrate spacing. Suitable epoxy resins andspacers for use in a perimeter seal member 118 are disclosed in U.S.patent application Ser. No. 08/834,783, entitled “An ElectrochromicMirror With Two Thin Glass Elements And A Gelled Electrochromic Medium”,which is hereby incorporated herein by reference.

The electrochromic medium 124 includes electrochromic anodic andcathodic materials that generally can be selected from the followingcategories:

(i) Single layer—the electrochromic medium is a single layer of materialwhich may include small nonhomogeneous regions and includes solutionphase devices where a material is contained in solution in the ionicallyconducting electrolyte and remains in solution in the electrolyte whenelectrochemically oxidized or reduced. Solution phase electroactivematerials may be contained in the continuous solution phase of a crosslinked polymer matrix in accordance with the teachings of U.S. Pat. Nos.5,679,283 and 5,888,431, both entitled “ELECTROCHROMIC LAYER AND DEVICESCOMPRISING SAME”, and U.S. application Ser. No. 08/616,967, entitled“IMPROVED ELECTROCHROMIC LAYER AND DEVICES COMPRISING SAME” orInternational Patent Application Serial No. PCT/US98/05570 entitled“ELECTROCHROMIC POLYMERIC SOLID FILMS, MANUFACTURING ELECTROCHROMICDEVICES USING SUCH SOLID FILMS, AND PROCESSES FOR MAKING SUCH SOLIDFILMS AND DEVICES”.

Prior art electrochromic media generally employed two electrochromiccompounds, one anodic and one cathodic, and were unable to acceptablyproduce gray shades, and numerous other shades of color as well. In U.S.application Ser. No. 08/837,596, filed Apr. 2, 1997, and entitled “ANIMPROVED ELECTROCHROMIC MEDIUM CAPABLE OF PRODUCING AN PRESELECTEDCOLOR” herein incorporated by reference, non-staging devices capable ofachieving a preselected color are disclosed. These devices contain atleast three electroactive materials, at least two of which areelectrochromic compounds, and exhibit little or no staging while beingavailable in neutral colors such as gray, or in other preselected colorsnot normally available.

The anodic and cathodic materials can be combined or linked by abridging unit as described in International Application Serial No.PCT/W097/EP498 entitled “ELECTROCHROMIC SYSTEM”. It is also possible tolink anodic materials or cathodic materials by similar methods. Theconcepts described in these applications can further be combined toyield a variety of electrochromic materials that are linked.

Additionally, a single layer medium includes the medium where the anodicand cathodic materials can be incorporated into the polymer matrix asdescribed in International Application Serial No. PCT/WO98/EP3862entitled “ELECTROCHROMIC POLYMER SYSTEM” or International PatentApplication Serial No. PCT/US98/05570 entitled “ELECTROCHROMIC POLYMERICSOLID FILMS, MANUFACTURING ELECTROCHROMIC DEVICES USING SUCH SOLIDFILMS, AND PROCESSES FOR MAKING SUCH SOLID FILMS AND DEVICES”.

Also included is a medium where one or more materials in the mediumundergoes a change in phase during the operation of the device, forexample a deposition system where a material contained in solution inthe ionically conducting electrolyte which forms a layer, or partiallayer on the electronically conducting electrode when electrochemicallyoxidized or reduced.

In these single layer devices the electrochromic medium 124 includes atleast one anodic and one cathodic material, with at least one beingelectrochromic. Generally the materials are colorless or nearlycolorless in their unactivated state, so that when the potentialdifference across the electrodes is zero the electrochromic medium iscolorless or nearly colorless. When a sufficient potential difference isapplied between the electrodes 116 and 120 the cathodic species arereduced at the cathode, i.e. accept electrons from the cathode. On theother hand anodic species are oxidized at the anode i.e., they donateelectrons to the anode. As the anodic and cathodic species in theelectrochromic medium 124 accept and donate electrons to and from theelectrodes 116 and 120, at least one species becomes colored. The anodicand cathodic species in medium 124 return to their unactivated statewhen they exchange electrons towards the center of chamber 122. Theactivated species can reach this “recombination zone” through variousroutes including diffusion of the activated forms themselves, diffusionof charge, migration etc. This self-erasing process allows the cell toclear when the potential is removed. As long as the potential applied islarge enough for the electrochemical oxidation and reduction to takeplace the electrochromic cell will be colored.

(ii) Multilayer—the medium is made up in layers and includes at leastone material attached directly to an electronically conducting electrodeor confined in close proximity thereto which remains attached orconfined when electrochemically oxidized or reduced. Examples of thistype of electrochromic medium are the metal oxide films, such astungsten oxide, iridium oxide, nickel oxide and vanadium oxide. A mediumwhich contains one or more organic electrochromic layers, such aspolythiophene, polyaniline or polypyrrole attached to the electrodewould also be considered a multilayer medium.

In addition the electrochromic medium may also contain other materialssuch as light absorbers, light stabilizers, thermal stabilizers,antioxidants, thickeners or viscosity modifiers or tint providingagents. Among ultraviolet stabilizer agents, known to stabilizeplastics, are the compound ethyl-2-cyano-3,3-diphenyl acrylate, sold byBASF (Parsippany, N.J.) under the trademark Uvinul N-35 and by AcetoCorporation (Flushing, N.Y., USA) under the trademark Viosorb 910; thecompound (2-ethylhexyl)-2-cyano-3,3-diphenyl acrylate, sold by BASFunder the trademark Uvinul N-539; the compound2-(2′-hydroxy-4′-methylphenyl)benzotriazole, sold by Ciba-Geigy Corp.under the trademark Tinuvin P®; the compound2-hydroxy-4-methoxybenzophenone, sold by American Cyanamid under thetrademark Cyasorb UV 9; and the compound 2-ethyl-2′-ethoxyoxalanilide,sold by Sandoz Color & Chemicals under the trademark Sanduvor VSU.

EC devices having as a component part an EC medium can be used in a widevariety of applications wherein the transmitted or reflected light ismodulated. Such devices include rear-view mirrors such as are used forvehicles; windows for the exterior of a building, home or vehicle;skylights for buildings including tubular light filters; windows inoffice or room partitions; display devices; contrast enhancement filtersfor displays; light filters for photographic devices and light sensors;and indicators for power cells and batteries.

Any electroactive material may be used in accord with this invention,preferred however are electrochromic materials, especially organicelectrochromic materials.

To further describe the invention we will briefly review some of theproperties of 5,10-dimethyl-5,10-dihydrophenazine, a commonly usedanodic electrochromic material with the structure

and having 16 π electrons in the neutral, colorless form.Electrochemical removal of one electron gives:

Further oxidation leads to:

This 2e− oxidized form has 14 π electrons.

For an anodic material in general, the energy required to remove anelectron will be related to several factors including the environment(solvation energy changes), orbital energy levels, and geometry changes.Electrochemical measurements such as cyclic voltammograms ordifferential pulse voltammograms give energies required to cause theredox process to occur.

Redox potentials are readily measured using a variety of standardelectrochemical techniques. Often, cyclic voltammetry is used, and theredox potential is taken as the average of the anodic and cathodic peakpotentials. However, the influence of electrode kinetics and ofbackground current can make it extremely difficult to accurately measurepotentials in this way, particularly when two redox processes occur atsimilar potentials (i.e.,<100 mV apart). In such cases, pulse methodssuch as differential pulse voltammetry are preferred. Differential pulsevoltammetry employs an applied waveform that consists of small pulsessuperimposed on a potential staircase. The current is not monitoredcontinuously; rather, it is sampled at a set time interval after eachpulse. Because the background current decays more quickly than does thecurrent attributed to the redox process, this delay essentiallyeliminates nonfaradaic (background) contributions. A typicaldifferential pulse voltammogram shows negligible background current anddistinct well-defined peaks from each redox process. The peak maximacorrelate directly with redox potentials. Using differential pulsevoltammetry, closely spaced redox processes can be resolved providedthat they differ by at least about 20 mV.

These changes in the electron configuration lead to changes in theelectronic absorption spectra of the material in the different oxidationstates. Electronic transitions between the ground and excited state of aconjugated organic molecule can also give insights into the nature ofthe conjugated electronic structure of the molecule. Generally, longwavelength transitions indicate more extended conjugation in themolecule. Additionally, a formal transfer of charge from one atom orpart of a molecule to another will lead to observed transitions.

In accordance with the present invention, compounds can be prepared withthe general formula:

A−X−B

with A and B being the same or different monomeric electrochromiccompound and X being the coupling unit that allows electroniccommunication (or interaction) between A and B. In its broadest senseelectronic communication means that the presence of A, or a change inits electronic configuration (e.g., by oxidation or reduction) willaffect the properties of B. In addition, three or more monomers can becoupled with an upper limit, usually up to about seven to ten monomers.

By coupling is meant bonding between monomeric electrochromic compoundswhich causes the coupled electrochromic compound to exhibitelectrochemical and/or spectral properties which show electronicinteraction between the two monomeric electrochromic compounds asopposed to behavior which is approximately the sum of the individualcontributions of monomeric electrochromic compounds. In many cases, thecoupling will be by means of a delocalized π-electron system which, atleast for certain contributing structures, extends between the coupledelectrochromic compounds. Thus, the coupling will usually beaccomplished by a covalent bond, by an aromatic ring system, or by aconjugated unsaturated system.

Coupling between A and B can be seen by one or more of: a)electrochemical behavior exhibiting more than one first electron redoxpotential, each being with respect to the first electron removed fromeach monomeric electrochromic compound, the redox potentials beingdifferent from the first redox potential of the uncoupled monomericelectrochromic compounds; or b) exhibiting a spectrum in any readilyaccessible oxidation state which is not merely the sum of the spectra ofthe monomeric electrochromic compound(s), but which exhibitssubstantially different absorption in terms of the absorbency(extinction coefficient), absorption spectrum (color), or both.

The monomeric electrochromic compounds useful in this invention can besubstituted and unsubstituted fused ring systems such as5,10-dihydrophenazine, 10-hydro-5,10-phenothiazine,10-hydro-5,10-phenoxazine, benzidines, triphenodioxazines,triphenodithiazines, various metallocenes, quinoxalinophenazines,phenylenediamines, benzimidazole azines, benzoxazole azines, carbazoles,and benzothiazole azines.

All these systems may be substituted with a wide variety ofsubstituents, including, without limitation, hydrocarbon groups such asC₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl, C₃₋₂₀ cycloalkyl, C₄₋₂₀cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ aralkyl, and the like. Each of thesehydrocarbon substituents may contain one or more heteroatoms in lieu ofor in addition to the carbon atoms in the ring or chain, as the case maybe, and each may be unsubstituted or substituted by functional andnon-functional groups such as hydroxyl, alkoxy, cyano, halo, carboxy,keto, aldehydo, nitro, ester, polyoxyalkyl, and the like. The base ringsmay also be fused to other ring systems, such as C₄₋₂₀ cycloalkyl, C₄₋₂₀cycloalkenyl, benzo, phenanthro, anthro, quinoxilino, etc. Theunsaturated hydrocarbons may have one or more points or unsaturation, ofthe same or different type.

Further ring substituents include alkenylether, i.e. vinylether, alkoxy,cyano, amino, hydroxyl, ester, amide, imide, keto, aldehydo, carbamide,thioether, thiocarbamide, etc. Alkyl, alkenyl, cycloalkenyl, arylgroups, and like groups contained in these substituents, for exampleketo groups R—C(O), follow the carbon atom limitations given in theprevious paragraph for these respective groups.

Most preferred monomeric electrochromic compounds include substitutedand unsubstituted 5,10-dihydrophenazines, phenothiazines, andphenoxazines. The resulting coupled compounds have the following generalstructures:

Where Y₁ and Y₂ are selected from O, S, and N—R₇; and

X represents a coupling group or unit such as C₁₋₃ alkyl, C₂₋₆ alkenyl,C₂₋₆ alkynyl, C₄₋₁₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀aralkyl; optionally containing heteroatoms; and

R₁ through R₇ are the same or different hydrocarbon groups such as C₁₋₂₀alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl, C₃₋₂₀ cycloalkyl, C₄₋₂₀cycloalkenyl, C₆₋₂₀ alkaryl, C₇₋₂₀ aralkyl; and the like

n is an integer from 1-3; and

m is an integer from 1-4.

Each of these hydrocarbon substituents may contain one or moreheteroatoms in lieu of or in addition to the carbon atoms in the ring orchain, as the case may be, and each may be unsubstituted or substitutedby functional and non-functional groups such as hydroxyl, alkoxy, cyano,halo, carboxy, keto, aldehydo, nitro, ester, amide, polyoxyalkyl, andthe like.

Coupling of monomeric electrochromic compounds may take place bystandard methods, i.e. by the reductive coupling of monomericelectrochromic compounds bearing reactive halo groups by reaction withactive metal, etc. Coupled electrochromic compounds may also besynthesized by forming the coupling group during synthesis of thecoupled electrochromic compound rather than by later coupling monomericelectrochromic compounds. Thus, if the target coupled electrochromiccompound molecule is a coupled2,3,5,10-tetramethyl-5,10-dihydrophenazine, coupled by a covalent bond,one suitable synthesis would start as follows:

followed by N-methylation at each of the 5,5′ and 10,10′ positions. Suchsyntheses are disclosed in U.S. application Ser. No. 09/280,396, hereinincorporated by reference.

The coupling may be through the ring carbons of the aromatic portions ofthe molecule, or where the monomeric electrochromic compound has anon-aromatic ring nitrogen or phosphorus, may be at this position, forexample from the 5 and/or 10 position of a 5,10-dihydrophenazine, or the10-position of a 10-phenoxazine.

The effects of the coupling are best shown by the electrochemical andspectral behavior. Monomeric electrochromic compounds such as5,10-dimethyl-5,10-dihydrophenazine, shown in FIG. 2, generally exhibittwo current peaks on oxidation which represent the loss of first andsecond electrons to produce 1+ and 2+ charged species, respectively.Similarly, a linked but non-coupled electrochromic compound willexhibit, based on the same total moles of monomeric electrochromiccompound, a voltammogram which will be very similar to that of asimilarly substituted monomeric electrochromic compound.

For example, the spectrum of the compound:

which is linked, but not coupled, should be substantially the same asthat of

Thus, the absorption spectrum of linked but non-coupled electrochromiccompounds should be substantially the same as the monomericelectrochromic compound, and the current/voltage behavior should bevirtually the same as well, exhibiting a single peak (similar to FIG. 2)which represents both the removal of a single electron from one half ofthe linked but non-coupled electrochromic compound and removal of afirst electron (two electrons total) from the other half of the linkedbut non-coupled electrochromic compound. In other words, both theseelectrons will be removed at substantially the same redox potential,i.e., independently of each other. The same is true for each of thesecond electrons for each half. The identity of these redox potentialsbetween the linked but non-coupled electrochromic compound and themonomeric electrochromic compound is also indicative of a lack ofcoupling between the two halves of the linked but non-coupledelectrochromic compound. In other words, the linkage between themonomeric electrochromic compounds is insufficient to cause anysubstantial difference in the energy levels of the molecular orbitals ofthe linked but non-coupled electrochromic compounds. The monomericelectrochromic compounds behave independently.

FIG. 3 illustrates the coupled electrochromic compound2,2′-bis(5,10-dimethyl-5,10-dihydrophenazine). In FIG. 3, two of themonomeric electrochromic compounds whose electrochemical behavior isshown in FIG. 2 were coupled through a covalent bond. That thesemolecules are coupled and not monomeric or even merely linked is shownby the two current peaks entered at +236 mV and +348 mV, whichcorrespond to removal of a first electron (from one half of the coupledelectrochromic compound), and a second electron (from the other half).Note that the first electron is removed more easily (at a less positiveredox potential) than the first electron (300 mV) of the monomericelectrochromic compound, and demonstrates the effect of the electroniccommunication. Further evidence of electronic communication is thatremoval of the second electron is more difficult in the coupled2,2′-bis(5,10-dimethyl-5,10-dihydrophenazine), (348 mV), despite thefact that the electron is being removed from a different half of thecoupled electrochromic compound. In other words, the removal of anelectron from the first half affects the properties of the other half.The same behavior is exhibited by the second electron removal from eachhalf (3^(rd) and 4^(th) electrons).

The electronic communication can occur via an extended π electronicsystem, a σ system or via through space effects. Extended π electronicsystems have proven to be very efficient in this coupling. Thus, theability of the two halves of the compound to show electroniccommunication is related to the geometric structure of the oxidized formof the material. Materials with strong communication will give result ina planar, or nearly planar, geometry and weak electronic communicationwill be non-planar or twisted geometry.

Dependence of the electronic communication on steric and distancefactors can be seen in FIG. 4 which shows the voltammogram for thelinked but not coupled compound1,4-bis(5,10-dihydro-5-butyl-10-phenazine)benzene. A limited electroniccommunication between the phenazine systems is consistent with the factthat the first separation of the two oxidation waves is not resolvable(less than 20 mV). We believe this is due to the steric interaction ofthe protons at the 1 and 9 positions of the phenazine and the hydrogenatoms on the linking benzene ring.

Further evidence of coupling is evident from the absorption spectrum ofthe coupled electrochromic compounds. Anodic electrochromic materialsexhibit a change in their extinction coefficient at least one wavelengthin the visible region of the electromagnetic spectrum on electrochemicaloxidation, and can be said to exhibit “electrochromic activity” at thosewavelengths. The coupled compounds of this invention exhibitelectrochromic activity at wavelengths where the monomeric compounds donot exhibit electrochromic activity when they have been oxidized to thesame “relative electron density” change. FIG. 5 shows an example of acoupled electrochromic compound that exhibits electrochromic activity atwavelengths where the anodic monomeric electrochromic compound does not.

FIG. 5a shows the absorption spectrum of5,10-dimethyl-5,10-dihydrophenazine cation, showing a weak band at about700 nm and the more intense band near 450 nm. FIG. 5b, by comparison,shows the absorption spectrum of2,2′-bis(5,10-dimethyl-5,10-dihydrophenazine) dication. The strongabsorbance in the near infrared region (900 nm) is a clear indicationthat the electronic states of this molecule are very different from themonomeric electrochromic compound. In this case the cation of themonomeric compound and the dication of the coupled compound have thesame relative electron density change.

FIG. 6a shows the absorption spectrum of1,4-bis(5,10-dihydro-5-butyl-10-phenazine)benzene. This compound withthe presumed large steric interaction severely limiting the electroniccommunication between the halves of the molecule shows an absorbancespectrum that has absorbance bands at roughly the same wavelengths asthe monomeric compound, 5,10-dimethyl-5,10-dihydrophenazine. It is notedhere that various alkyl groups, and the phenyl group in place of themethyl groups in the 5,10-dihydrophenazines do not change the absorbancespectrum of the phenazine cation to a great extent.

In the case of 2,2′-bisphenazines, the presence of a closed shell πelectron system involving both of the monomeric electrochromic compoundsin the +2 oxidation form is a reasonable explanation for the effects onthe voltammogram and absorption spectrum. Thus the reduced form:

can be oxidized to the dication, a resonance structure of which can bewritten:

This closed shell resonance form contains no radicals, and molecularorbital calculations such as AMPAC predict that this resonance form isimportant in the consideration of the atomic and electronic structure ofthe compound.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLE 1 Synthesis of 5,5′,10,10′-tetramethyl-2,2′-bisphenazine

To a 100 ml 3-necked round bottom flask 4.3 g 3,3′-diaminobenzidine and13.2 g catecol were mixed, and the mixture heated to 150° C. for 16hours. The mixture was then cooled to 100° C., and 50 ml of water added.The solution was heated to reflux for 1 hour, cooled, and the solidtetrahydrobis(phenazine) isolated by filtration. Alkylation of thetetrahydrobis(phenazine) was accomplished by the method described inU.S. patent application Ser. No. 09/280,396.

EXAMPLE 2 Syntheses of 5,5′,10,10′-tetramethyl-2,2′-bis[a]benzophenazine

In a 3-necked round bottom flask 7.9 g 1,2-naphthoquinone was dissolvedin 100 ml acetic acid and heated to 60° C. 5.0 g of3,3′-diaminobenzidine was dissolved in 200 ml ethanol and the 100 mlacetic acid containing the naphthoquione was dripped into the benzidinesolution followed by stirring at 60° C. for 2.5 hours. The mixture wasthen cooled and the solid bisphenazine separated by filtration.Alkylation of the bisphenazine was accomplished by preparing a 3:1mole:mole alloy of K:Na in refluxing toluene. After the mixture cooled,the toluene was removed, and dimethoxyethane added. The bisphenazine wasadded in a 1:10 mole:mole ratio with the alloy, and the mixture wasallowed to stir for 2 hours at 50° C. Methyl iodide was added, and theproduct isolated by standard techniques.

EXAMPLE 3 Alkylation of5,5′,10,10′-tetramethyl-2,2′-bis[b]benzophenazine

2,2′-bis[b]benzophenazine was prepared analogously to thebenzo[a]phenazine of Example 2. Alkylation of the bisphenazine wasaccomplished by preparing a 3:1 mole:mole alloy of K:Na in refluxingtoluene. After the mixture cooled, the toluene was removed, anddimethoxyethane added. The bisphenazine was added in a 1:10 mole:moleratio with the alloy and the mixture was allowed to stir for 2 hours at50° C. Methyl iodide was added, and the product subsequently isolated.

EXAMPLE 4 Syntheses of5,5′,10,10′-tetramethyl-2,2′-bis[a,c]benzophenazine

11.5 g phenanthroquinone was dissolved in 400 ml acetic acid and heatedto 105° C. 5.4 g of 3,3′-diaminobenzidine was dissolved in 200 mlethanol and the 400 ml acetic acid containing phenanthraquinone wasdripped into the benzidine solution, and was stirred at 100° C. for 1hour. The mixture was then cooled, and the solid bisphenazine separatedby filtration. Alkylation of the bisphenazine was accomplished byforming a 3:1 mole:mole alloy of K:Na in refluxing toluene. After themixture cooled, the toluene was removed, and dimethoxyethane added. Thebisphenazine was added in a 1:10 mole:mole ratio with the alloy, and themixture allowed to stir for 2 hours at 50° C. Methyl iodide was addedand the product isolated.

EXAMPLE 5 Syntheses of 5,5′,10,10′-tetrahydro-bis(5,5′-dibutylphenazine)-1,4-benzene

6.6 g 1,4-diiodobenzene was dissolved in 100 ml diethylether and cooledto 0° C. in argon atmosphere. 18 ml 2.5M n-butyllithium solution wasadded over a period of 15 minutes while carefully excluding air. Themixture was stirred for 10 minutes. 9.0 g of phenazine was then addedover a period of 2 hour following which the mixture is stirred for 1hour at 0° C. A solution of iodobutane in THF was added and the solutionallowed to warm to room temperature. The product, containing two5-butyl-5,10-dihydrophenazine electrochromic compound molecules linkedat the 10,10′ positions by a 1,4-phenyl coupling group, was thenisolated.

EXAMPLE 6 Synthesis of 5,5′,10,10′-tetrahydro-5,5′,10,10′-tetrabutyl2,2′bis(7,7′-trifluoromethylphenazine) and5,5′,10,10′-tetrahydro-5,5′,10,10′-tetrabutyl2,2′bis(8,8′-trifluoromethylphenazine)

21.4 g 3,3′-diaminobenzidine, 54.0 g of 4-bromo-3-nitrobenzotrifluorideand 21.2 g Na₂CO₃ were added to 200 ml DMF in a 500 ml round bottomflask. The mixture was heated to 120-130° C. for 16 hours. The mixturewas then cooled, water added, and product extracted into an ethylacetate layer. The ethyl acetate was then evaporated off. The residuewas then dissolved in 200 ml of methanol, and this solution added to asolution of 75.9 g SnCl₂ dissolved in 100 ml conc. HCl. The mixture washeated to 60-70° C., the temperature being maintained for 16 hours. Anadditional 35 g SnCl₂ was added and the mixture stirred for 4 hours at60-70° C. The methanol was evaporated, and the pH of the solution isgradually increased by adding NaOH, followed by another extraction intoethyl acetate. The ethyl acetate was evaporated, and the resultingmaterial dissolved in 500 ml methanol. To this solution 162.2 g of FeCl₃was slowly added, and the mixture heated to reflux. The reaction mixturewas cooled and water added, and the bisphenazine filtered off as a darksolid. The bisphenazine was alkylated by the method described in Example1.

EXAMPLE 7 Synthesis of5,5′,10,10′-tetrahydro-bis(5,5′-diphenylphenazine)-1,4-buta-(1,3)-diyne

4.5 g phenazine was dissolved in 100 ml dimethoxyethane and cooled to 0°C. in a nitrogen atmosphere. 16.7 ml 1.8M phenyllithium was added over aperiod of 10 minutes, carefully excluding air. The mixture is stirredfor 1.5 hours. 1.7 g KOH and 30 ml DMSO were added to the resultingslurry and stirred for 1 hour. 6.4 g trifluoroethyliodide was added andthe mixture was left to stir for 10 days at room temperature. Theproduct was isolated and characterized by mass spectral analysis andcyclic voltametry.

EXAMPLE 8 Synthesis of bis1,2-(5,10-tetrahydro-5,10-dimethylphenazine)ethene

The synthesis of the bisphenazine ethene was accomplished via the directcoupling of 2-formyl-5,10-dihydro-5,10-dimethyphenazine viaamodification of the process described (JACS (117)p. 4468-4475, 1995).The 2-formyl compound was coupled using TiCl₄ and Zn in THF/Pyridinegave the desired compounds.

EXAMPLE 9 Synthesis of5,5′,10,10′-tetrahydro-5,5′,6,6′,10,10′-hexamethyl-2,2′-bisphenazine

10.0 g 3,3′-diaminobenzidine and 34.7 g 3-methylcatechol were mixedtogether in 40 ml ethylene glycol in a 500 ml round bottom flask. Themixture was heated to reflux. The reaction mixture was cooled to 80° C.and 400 ml water was then added, and the mixture reheated to reflux. Thereaction mixture was cooled to room temperature. After two washes withwater, the solid was filtered and dried overnight.

Alkylation of the material was accomplished via the one-pot synthesisdescribed in Example 1. The final product was characterized byelectrochemical methods to have oxidation waves at 280, 376,976, and1092 mV (on a scale where the first oxidation of5,10-dimethyl-5,10-dihydrophenazine is assigned a value of 300 mV).

EXAMPLE 10 Synthesis of5.5′,7(8),7′(8′),10,10′-hexamethyl-2,2′-bisphenazine

10.0 g 3,3′-diaminobenzidine and 34.7 g 4-methylcatechol were mixedtogether in 40 ml ethylene glycol in a 500 ml round bottom flask. Themixture was heated to reflux for 24 hours. The temperature drops to203°, and using a Dean Stark condenser, 5 ml of ethylene glycol wasremoved and the mixture allowed to reflux for an additional 24 hours.The reaction mixture was cooled to 80° and 250 ml water added, followingwhich the reaction mixture was cooled to room temperature. After threewashes with water, the solid was separated by filtration.

Alkylation of the material was accomplished via the one-pot synthesisdescribed in Example 1. The final product was characterized byelectrochemical methods to have oxidation waves at 200, 308, 924 and1044 mV (on a scale where the first oxidation of5,10-dimethyl-5,10-dihydrophenazine is assigned a value of 300 mV).

EXAMPLE 11 Synthesis of 10,10′-dimethyl-3,3′-bisphenothiazine

2.0 g N,N′-diphenylbenzidine, 0.57 g sulfur and 0.3 g iodine were heatedto 210°. After most of the starting material was converted, 10 ml xyleneand 0.2 g sulfur are added and the mixture allowed to reflux for 16hours. The reaction mixture was cooled to room temperature, 40 mlbenzene added to the mixture, and the solid product isolated byfiltration. Alkylation of the material was accomplished as described inExample 1.

EXAMPLE 12

An electrochromic window was prepared from two pieces of LOF TEC glassspaced apart 250 microns with an epoxy seal, and vacuum filled with asolution of 16 mM methyl viologen tetrafluoroborate, 8 mM5,5′,10,10′-tetrahydro-5,5′,10,10′-tetramethyl 2,2′-bisphenazine, and 30mM Tinuvin-P® in propylene carbonate with 3 weight percent PMMA.

The device exhibited a transmittance (Y D65/2) of 72% initially and withapplication of 1.2V the transmittance decreased to 4% in about 20seconds. Shorting the electrodes of the device restored the device toits original transmittance level.

The device was cycled in an Atlas Weather-Ometer operating at 0.55W/m²nm at 340 nm for 1614 hours. After this period the transmittance wasreduced only slightly, to 63%. Application of 1.2V decreased thetransmittance of the device to 4.3%. Shorting the electrodes of thedevice returned the transmittance to 63%.

EXAMPLE 13

A solution of 2 mM 2,2′-bis-DMP in propylene carbonate was oxidized tothe +2 state and flame-sealed into an evacuated glass tube. The tube wasplaced in a Weather-Ometer operating at 0.55 W/m²nm at 340 nm for 2645hours. The tube was then opened and DPV run on the solution. Theelectrochemistry showed very little change compared with a sample ofnon-irradiated 2,2′-bis-5,10-dimethyl-5,10-dihydrophenazine.

What is claimed is:
 1. An electrochromic medium comprising two or moreelectroactive compounds, at least one of said electroactive compoundsbeing a coupled electrochromic compound comprising a first anodicmonomeric electrochromic compound coupled by a bridge comprising acovalent bond or an intervening hydrocarbon structure optionallycontaining one or more heteroatoms, to a second anodic monomericelectrochromic compound, and optionally additional monomericelectrochromic compounds such that electronic communication is exhibitedbetween said anodic monomeric compounds.
 2. The electrochromic medium ofclaim 1, wherein said first anodic monomeric electrochromic compound andsaid second anodic monomeric electrochromic compound are independentlyselected from the group consisting of substituted or unsubstituteddihydrophenazines, benzidines, phenothiazines, phenoxazines,triphenodioxazines, triphenodithiazines, quinoxalinophenazines,phenylenediamines, benzimidazole azines, benzoxazole azines, carbazoles,benzothiazoles, and mixtures thereof.
 3. The electrochromic medium ofclaim 1 wherein said first anodic monomeric electrochromic compound andsaid second anodic monomeric electrochromic compound are optionallysubstituted 5,10-dihydrophenazines.
 4. The electrochromic medium ofclaim 1 wherein the said coupled electrochromic compound is selectedfrom one of the following structures:

where Y₁ and Y₂ are selected from O, S, and N—R₇; and X represents acoupling group or unit such as C₁₋₃ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl,C₄₋₁₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀ aralkyl; optionallycontaining heteroatoms; and R₁ through R₇ are the same or differenthydrocarbon groups such as C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl,C₃₋₂₀ cycloalkyl, C₄₋₂₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀aralkyl; and the like n is an integer from 1-3; and m is an integer from1-4.
 5. An electrochromic device which comprises an electrochromicmedium of claim
 1. 6. An electrochromic medium comprising two or moreelectroactive compounds, at least one of said electroactive compoundsbeing a coupled electrochromic compound comprising a first anodicmonomeric electrochromic compound coupled by a bridge comprising acovalent bond or an intervening hydrocarbon structure optionallycontaining one or more heteroatoms to a second anodic monomericelectrochromic compound, and optionally additional anodic monomericcompounds such that the absorption spectrum of said coupledelectrochromic compound is different from the sum of the absorptionspectrum of a mixture of the individual anodic monomeric compounds on anidentical mole basis.
 7. The medium of claim 6 wherein said first anodicmonomeric electrochromic compound and said second anodic monomericelectrochromic compound are independently selected from the groupconsisting of substituted or unsubstituted dihydrophenazines,benzidines, phenothiazines, triphenodioxazines, phenoxazines,triphenodithiazines, quinoxalinophenazines, phenylenediamines,benzimidazole azines, benzoxazole azines, carbazoles, benzothiazolesazines, and mixtures thereof.
 8. The medium of claim 6 herein the saidcoupled compound is selected from the group consisting of:

where Y₁ and Y₂ are selected from O, S, and N—R₇; and X represents acoupling group or unit such as C₁₋₃ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl,C₄₋₁₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀ aralkyl; optionallycontaining heteroatoms; and R₁ through R₇ are the same or differenthydrocarbon groups such as C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl,C₃₋₂₀ cycloalkyl, C₄₋₂₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀aralkyl; and the like n is an integer from 1-3; and m is an integer from1-4.
 9. The medium of claim 6 wherein said first anodic monomericelectrochromic compound and said second anodic monomeric electrochromiccompound are optionally substituted 5,10-dihydrophenazines.
 10. Anelectrochromic medium comprising two or more electroactive compounds, atleast one of said electroactive compounds being a coupled electrochromiccompound comprising a first anodic monomeric electrochromic compoundcoupled by a bridge comprising a covalent bond or an interveninghydrocarbon structure optionally containing one or more heteroatoms to asecond anodic monomeric electrochromic compound such, and optionallyadditional anodic monomeric electrochromic compounds that thevoltammogram of said coupled electrochromic compound is measurablydifferent from said anodic monomeric compounds when run in the samesolvent.
 11. The medium of claim 10 wherein said first anodic monomericelectrochromic compound and said second anodic monomeric electrochromiccompound are independently selected from the group consisting ofsubstituted or unsubstituted dihydrophenazines, benzidines,phenothiazines, triphenodioxazines, phenoxazine, triphenodithiazines,quinoxalinophenazines, phenylenediamines, benzimidazole azines,benzoxazole azines, carbazoles, benzothiazole azines, and mixturesthereof.
 12. The electrochromic device of claim 11 wherein said deviceis an electrochromic window.
 13. The medium of claim 10 wherein saidfirst anodic monomeric electrochromic compound and said second anodicmonomeric electrochromic compound are optionally substituted5,10-dihydrophenazines.
 14. The medium of claim 10 wherein the coupledelectrochromic compound is selected from the group consisting of:

where Y₁ and Y₂ are selected from O, S, and N—R₇; and X represents acoupling group or unit such as C₁₋₃ alkyl, C₂₋₆ alkenyl, C₂₋₆ alkynyl,C₄₋₁₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀ aralkyl; optionallycontaining heteroatoms; and R₁ through R₇ are the same or differenthydrocarbon groups such as C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl,C₃₋₂₀ cycloalkyl, C₄₋₂₀ cycloalkenyl, C₆₋₂₀ aryl, C₇₋₂₀ alkaryl, C₇₋₂₀aralkyl; and the like n is an integer from 1-3; and m is an integer from1-4.
 15. An electrochromic device comprising: a first transparentsubstrate, a second substrate, a sealing member disposed between saidfirst and second substrates to define a chamber; an electrochromicmedium disposed in said chamber, said electrochromic medium comprisingtwo or more electroactive compounds, at least one of said electroactivecompounds being a coupled electrochromic compound comprising a firstanodic monomeric electrochromic compound coupled by a bridge to a secondanodic monomeric electrochromic compound, such that electroniccommunication is exhibited between said first anodic compound and saidsecond anodic compound.
 16. An electrochromic device comprising: a firsttransparent substrate, a second substrate, a sealing member disposedbetween said first and second substrates to define a chamber; anelectrochromic medium disposed in said chamber, said electrochromicmedium comprising two or more electroactive compounds, at least one ofsaid electroactive compounds being a coupled electrochromic compoundcomprising a first anodic monomeric electrochromic compound coupled by abridge to a second anodic monomeric electrochromic compound, such thatthe absorption spectrum of said coupled electrochromic compound isdifferent from the sum of the absorption spectrum of a mixture of theindividual first and second anodic electrochromic compound on anidentical mole basis.
 17. An electrochromic device comprising: a firsttransparent substrate, a second substrate, a sealing member disposedbetween said first and second substrates to define a chamber; anelectrochromic medium disposed in said chamber, said electrochromicmedium comprising, two or more electroactive compounds, at least one ofsaid electroactive compounds being a coupled electrochromic compoundcomprising a first anodic monomeric electrochromic compound coupled by abridge to a second anodic monomeric electrochromic compound, such thatthe voltammogram of said coupled electrochromic compound is measurablydifferent from said first and second monomeric electrochromic compoundswhen run in the same solvent.
 18. A coupled electrochromic compoundcomprising a first anodic monomeric electrochromic compound coupled by abridge to a second anodic monomeric electrochromic compound such thatthe absorption spectrum of said coupled electrochromic compound at thesame relative electron density change as the monomeric compounds has atleast one absorption band that is absent in the monomeric electrochromiccompounds.
 19. A coupled electrochromic compound comprising a firstanodic monomeric electrochromic compound coupled by a bridge comprisinga covalent bond or an intervening hydrocarbon structure optionallycontaining one or more heteroatoms to a second anodic monomericelectrochromic compound such that the absorption spectrum of saidcoupled electrochromic compound at the same relative electron densitychange as the monomeric compounds exhibits electrochromic activity atleast one wavelength different from the monomeric compounds.
 20. Acompound of claim 19 wherein the said wavelength is in the near-infraredportion of the electromagnetic spectrum.